Adaptive LPC noise reduction system

Abstract

A noise suppression system reduces low-frequency noise in a speech signal using linear predictive coefficients in an adaptive filter. A digital filter may update or adapt a limited set of linear predictive coefficients on a sample-by-sample basis. The linear predictive coefficients may be used to provide an error signal based on a difference between the speech signal and a delayed speech signal. The error signal represents an enhanced speech signal having attenuated and normalized low-frequency noise components.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]This disclosure relates to noise suppression. In particular, this disclosure relates to reducing low-frequency noise in speech signals.[0003]2. Related Art[0004]Users access various systems to transmit or process speech signals in a vehicle. Such systems may include cellular telephones, hands-free systems, transcribers, recording devices and voice recognition systems.[0005]The speech signal includes many forms of background noise, including low-frequency noise, which may be present in a vehicle. The background noise may be caused by wind, rain, engine noise, road noise, vibration, blower fans, windshield wipers and other sources. The background noise tends to corrupt the speech signal. The background noise, especially low-frequency noise, decreases the intelligibility of the speech signal.[0006]Some systems attempt to minimize background noise using fixed filters, such as analog high-pass filters. Other systems attempt to sele...

AI Technical Summary

Benefits of technology

[0007]A noise suppression system reduces low-frequency noise in a speech signal using linear predictive coefficients in an adaptive filter. A digital filter may update or adapt a limited set of linear predictive coefficients on a sample-by-sample basis. The linear predictive coefficients may model the human vocal tract. The linear predictive coefficients may be used to provide an error signal based on a difference between the speech signal and a delayed speech signal. The error signal may represent an enhanced speech signal having attenuated and normalized low-frequency noise components.

Problems solved by technology

The background noise tends to corrupt the speech signal.

The background noise, especially low-frequency noise, decreases the intelligibility of the speech signal.

The fixed filters may indiscriminately eliminate desired signal content, and may not adapt to changing amplitude levels.

Low-frequency noise, even if lower in amplitude than the speech signal, tends to mask or reduce the intelligibility of speech.

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